1. Field of the Invention
Embodiments of the invention relate to a liquid crystal display and a method for driving the same capable of reducing power consumption of a data driving circuit.
2. Discussion of the Related Art
Liquid crystal displays display an image by adjusting light transmittances of liquid crystal cells in response to a video signal. An active matrix type liquid crystal display switches on or off a data voltage supplied to liquid crystal cells using a thin film transistor (TFT) formed in each of the liquid crystal cells to thereby actively control data. Therefore, display quality of the active matrix type liquid crystal display may increase.
The liquid crystal display inverts a charging polarity of the data voltage every predetermined liquid crystal cells, so as to reduce a direct current (DC) offset component and to reduce degradation of liquid crystals. However, every time the charging polarity of the data voltage is inverted in an inversion driving scheme, a swing width of the data voltage supplied to data lines increases, and a heat generation temperature of a data driving circuit increases. As a result, power consumption of the data driving circuit greatly increases.
A charge sharing method illustrated in FIGS. 1A and 1B has been proposed, so as to reduce the swing width of the data voltage, to reduce the heat generation temperature of the data driving circuit, and to achieve low power consumption. The charge sharing method turns on a charge sharing switch SW1 connected between adjacent output channels of the data driving circuit during a high logic level period of a source output enable SOE and shares positive charges and negative charges with one another inside a liquid crystal display panel, thereby changing an initial output level of the data driving circuit to a middle level.
The application of the charge sharing method does not always reduce the power consumption of the data driving circuit. The charge sharing method generally reduces the power consumption of the data driving circuit when a data pattern, of which data successively output through the same channel has a large gray level difference, is displayed. On the other hand, the charge sharing method increases the power consumption of the data driving circuit when a data pattern, of which data has a small gray level difference, is displayed.
In the related art, as shown in FIG. 2, a charge sharing function was unconditionally activated irrespective of characteristics of a data pattern input to the data driving circuit, and a polarity inversion period of the data voltage successively output through the same channel was fixed to k horizontal period, where k is a positive integer. FIG. 2 illustrates an output swing width of the data driving circuit when the liquid crystal display implements a full black pattern by activating the charge sharing function in the liquid crystal display panel, which operates in a normally white mode (representing a low gray level as a voltage level difference between the data voltage and a common voltage increases), and applying the data voltage to the data driving circuit in a vertical 2-dot inversion scheme (inverting the polarity of the data voltage every two horizontal periods). In the normally white mode, the output swing width of the data driving circuit has a maximum value when the full black pattern is implemented. In FIG. 2, ‘Vdd’ and ‘Vss’ denote power voltages for determining an output range of the data driving circuit, and ‘Vcom’ denotes the common voltage of the liquid crystal display panel.
In the related art, the data voltage swings between the power voltages Vdd (i.e., a positive maximum power voltage) and Vss (i.e., a negative maximum power voltage) every two horizontal periods, so as to implement the vertical 2-dot inversion scheme under the above-described conditions. Further, the data voltage has to swing between the positive maximum power voltage Vdd and the common voltage Vcom or between the negative maximum power voltage Vss and the common voltage Vcom in units of one horizontal period, so as to implement the charge sharing method under the above-described conditions. Thus, because the number of swing operations of the data voltage increases, it is difficult to reduce the power consumption of the data driving circuit.